There are known processes comprising exposing a light-sensitive laminate, wherein a peel layer comprising an organic polymer and a light-sensitive resin layer are provided on a provisional substrate, developing said laminate so as to form an image on the peel layer and then transferring said image onto an arbitrary substrate (described, e.g., in JP-B-46-15326 and JP-B-49-441, which corresponds to U.S. Pat. No. 3,721,557; the term "JP-B" as used herein means an "examined Japanese patent publication"). These processes are advantageous in that they can be applied as a color proof both of over-lay type and surprint type. However, they suffer from some disadvantages, such as that an adhesive should be used for each transfer, which makes the procedure troublesome, and that it is difficult to achieve a high accuracy at site-matching in the transfer of each color.
JP-A-47-41830, JP-A-48-93337 and JP-A-51-5101 each propose a process for relieving the troublesome procedure by adhering a formed image to an image-receiving sheet and applying heat and pressure to said image-receiving sheet so as to transfer said image. The term "JP-A" as used herein means "unexamined published Japanese patent application". JP-A-51-5101 discloses, in particular, a process wherein a hot-melt polymer layer is provided as an adhesive on a temporary substrate, while JP-A-47-41830 discloses a process for directly transferring an image onto a permanent substrate such as art paper or coated paper.
However, these processes have several disadvantages. One disadvantage resides in that the final image obtained thereby is reversed right and left with respect to the original. Another disadvantage resides in that the use of a hot-melt polymer of a high melting point requires an elevated transfer temperature, which lowers the dimensional stability of the substrate and causes a shift in site-matching at the transfer of each color. When a polymer of a low melting point is employed, on the other hand, problems such as adhesion after the formation of an image or the occurrence of marks frequently occur. In order to overcome these disadvantages, JP-A-59-97140, which corresponds to U.S. Pat. No. 4,482,625, discloses a process wherein an image of each color is once transferred onto an image-receiving sheet provided with a photopolymerizable image-receiving layer, and then said image is retransferred onto the permanent substrate followed by hardening said photopolymerizable image-receiving layer through exposure.
The image obtained by this process is positive with respect to the mask original. Further, the photopolymerizable image-receiving layer containing an ethylenically polyfunctional monomer is soft per se. Thus the transfer can be effected at a low temperature and the photopolymerizable image-receiving layer is hardened thereafter by exposure, which makes said layer highly resistant against adhesion and marks. Therefore, most of the above-mentioned disadvantages are overcome thereby.
The image-receiving sheet is provided to users as the image-receiving layer is provided with a cover sheet so as to prevent said image-receiving layer from staining and marks. Thus, the cover sheet should be removed by users immediately before use.
However, the use of a conventional cover sheet suffers from several problems, as described below.
(1) When an image is to be transferred from the image-forming material to the image-receiving sheet, poor slip between the image-receiving layer surface of the image-receiving sheet and the image-forming material sometimes causes contamination bubbles between them, which results in the deterioration of the image, which is a fatal injury in the case of a color proof.
(2) Poor slip between the substrate of the image-receiving sheet and a cover sheet or between cover sheets can make handling difficult.
(3) When the image-receiving sheet is exposed to ultraviolet light during prolonged storage, the transferability is sometimes deteriorated.
(4) It is difficult to tell which is the face of the image-receiving sheet element, which makes the workability poor.
(5) With the lapse of time, additives contained in the image-receiving sheet would migrate toward the surface of the cover sheet, which is accompanied by the deterioration in the performance of the image-receiving sheet and staining of the surface. Further, the transferability is deteriorated by moisture or air penetrating from the outside.
(6) Static electricity makes it difficult to peel the cover sheet from the image-receiving sheet. Furthermore, static electricity sometimes makes the cover sheet after peeling electrostatic, so as to stick to the image-receiving sheet, substrate, or hands.